1. Field of the Invention
The invention relates to a method of electrically and mechanically connecting an electrical conductor wire to a hook-shaped element of an electrically conductive supporting body, the conductor wire, which comprises an electrically conductive core and a sheath of an insulating material, being introduced into the open hook-shaped element, upon which the hook-shaped element is closed under pressure.
The invention also relates to a rotor for an electrical machine, which rotor comprises a rotor winding and a commutator, and to a stator for an electrical machine, which stator comprises a stator winding and a connecting member.
2. Description of Prior Art
A method as defined above is disclosed in EP-0,280,386 which corresponds to U.S. Pat. No. 4,835,430, (herewith incorporated by reference). In accordance with the prior-art method a wire of a rotor coil is connected to a hook of a commutator segment by means of an electric current. For this purpose the wire is wrapped around the hook, after which the hook and the commutator segment are connected to electrodes. One of the electrodes is in contact with the commutator segment and another electrode is in contact with the hook, which is thus closed. An electric current is applied between the electrodes to heat the hook, the heat thus produced causing the insulation layer to be burnt off the wire and electrical contact to be established between the wire and the hook.
A drawback of the prior-art method is that during connection of the wire to the hook the hook and hence the adjacent constructional parts are heated to a high temperature, so that a comparatively large surrounding area is heated. In modern equipment comprising, for example, temperature-sensitive electronic devices such a thermal load is often impermissible. Moreover, the high temperatures impose limitations on the choice of the materials for the constructional parts.
EP-A 0,280,386 also discloses a rotor for an electrical machine, comprising a rotor winding and a commutator, a conductor wire of the rotor winding being connected to a hook-shaped element of the commutator. It is noted that DE-A 2,328,698 which corresponds to British Patent 1,428,054 discloses a method of connecting an armature wire to a commutator, the bare armature wire being introduced into an open hook of a commutator segment, after which the free end of the hook is bent towards the segment. The armature wire is then flattened to establish metallic contact between the armature wire and the segment. It is to be noted also that U.S. Pat. No. 4,671,848 describes a method of locally removing a dielectric coating from a wire by means of a high-energy radiation source such as a laser. Finally, it is to be noted that from DE-A 3,542,380 (herewith incorporated by reference) it is known per se to use a laser beam in a method in which a coil lead of a rotor winding and a commutator hook are welded to one another. In accordance with this known method the coil lead is introduced into a recess formed in the commutator hook, after which the lead is bent. After the commutator hook has been closed a pulsating or non-pulsating laser beam is aimed at the coil lead via the recess to form a weld between the coil lead and the commutator hook.
It is an object of the invention to improve the method defined in the opening paragraph in such a manner that no heating or only local heating is necessary to connect a conductor wire to a hook-shaped element.
To this end the method in accordance with the invention is characterized in that after introduction of the conductor wire into the open hook-shaped element a radiation beam is aimed at the conductor wire in the open hook-shaped element to ablate the insulating material, after which, upon the ablation, the conductive core of the conductor wire is clamped in the hook-shaped element by cold deformation of the hook-shaped element. Ablation is to be understood to mean removal as a result of melting, evaporation, burning or pulverising or a combination of two or more of these processes. The wavelength of the radiation used for this purpose may lie in the UV and/or IR region. When UV radiation is used the insulating material is pulverised.